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Tin-doped goethites obtained by a simple method at ambient pressure and 70 °C were characterized by inductively coupled plasma atomic emission spectrometry, scanning electron microscopy, Rietveld refinement of powder X-ray diffraction data, and 57 Fe and 119 Sn Mossbauer spectroscopy. The particles size and the length to width ratios decreased with tin-doping. Sn partially substituted the Fe(III) ions provoking unit cell expansion and increasing the crystallinity of the particles with enlarged domains that grow in the perpendicular and parallel directions to the anisotropic broadening (1 1 1) axis. Intermetallic E, E′ and DC distances also change although the variations are not monotonous, indicating different variations in the coordination polyhedron. In general, the Sn-substituted samples present larger intermetallic distances than pure goethite, and the greatest change is shown in the E′ distance which coincides with the c -parameter. 119 Sn Mossbauer spectroscopy revealed that Sn(II) is incorporated as Sn(IV) in the samples. On the other hand, Fe(II) presence was not detected by 57 Fe Mossbauer spectroscopy, suggesting the existence of vacancies in the Sn-doped samples. A lower magnetic coupling is also evidenced from the average magnetic hyperfine field values obtained as tin concentration increased.

Joining of seamless, low carbon, steel tubes were performed by means of Transient Liquid Phase Bonding process employing a foil of Fe-Si-B metallic glass as filler material. The influence of the main parameters of the process was evaluated: temperature, holding time, pressure and post weld heat treatment. Powder samples were obtained from the joint of tubes and characterized employing Mossbauer Spectroscopy in transmission geometry. The sampling was performed both in tubes successfully welded and in those which show joint defects. The results obtained are correlated with the obtained microstructure and the diffusion of Si and B during the process.

Seamless carbon steel tubes were joined by the transient liquid phase (TLP) bonding process using Cu foilsas interlayers. Bonding was performed at 1300 °C for 7 min with an applied uniaxial pressure of 5 MPa. Thecompletion of isothermal solidification was not systematically achieved along the joint, leading to the presenceof athermally solidified liquid (ASL). Consequently, the ability to predict the time to complete isothermalsolidification ? and therefore its kinetics ? is of great interest. For this purpose, a one-dimensional modelusing the finite element method was employed to simulate the TLP bonding. In particular, regions where thecompletion of the process was not achieved provided a source for the effective diffusion coefficient (Def) forthe bonding process. By knowing Def, different cases were considered within the proposed model, from theremaining time to complete the bonding process for an observed ASL, to the maximum liquid gap that can beisothermally solidified for a selected holding time. The validity of the utilization of Def was confirmed by analysingthe diffusion kinetic regime of Cu in steel. Fil: Di Luozzo, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Boudard, Miguel Santiago. Centre National de la Recherche Scientifique; Francia Fil: Fontana, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina Fil: Arcondo, Bibiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentina

Ionic conducting glasses are used as electrolytes in electrochemical applications (microbatteries, sensors, etc.). An interesting superionic amorphous alloy is Ge–Se–Ag where the conducting species is the Ag + ion. This system is a good glass forming material which does not need high cooling velocities in a wide concentration range in the Se-rich corner. A maximum Ag content of 30 at.% could be introduced into a Se-rich sample with the composition GeSe 3 while still retaining the vitreous character. X-ray scattering curves are characterised by a first scattering peak (FSP) located at q ≈1 A −1 which corresponds to an intermediate range order [J. Non-Cryst. Solids 273 (2000) 30]. The fundamental structural unit of the glass is the GeSe 4/2 tetrahedra. In this work, we study the electric behaviour of the amorphous GeSeAg system. Glasses of the (GeSe 3 ) 100− x Ag x system were prepared in the composition range from x =0 to 25 at.%. The electrical characterisation was performed using AC voltages with frequencies ranging from 100 Hz to 100 KHz. The conductivity ( σ ≈10 −4 Ω −1 cm −1 for x =25 at room temperature) shows a monotonous decrease with decreasing Ag concentration. We discuss the relation between the glass structure and their electrical properties.

Ge y Se (1―y) glasses are semiconductors but when Ag is added above certain threshold concentration, Ag x [Ge y Se (1―y) ] (100―x) glasses behave as fast ionic conductors [Urena et al., Solid State lonics 176 (2005) 505]. This peculiar behavior may be attributed to the intrinsically inhomogeneous nature of these glasses where zones rich in metals coexist with zones of the host material. The conductivity transformation may be ascribed to the percolation of the Ag rich phase [Pradel et al., J. Phys.: Condens. Matter 15 (2003) S1561]. Ag x [Ge 0.25 Se 0.75 ] (100―x) glasses either massive or as films were obtained by melt quenching and pulsed laser deposition (PLD), respectively, in compositions belonging to the Se rich corner of the ternary phase diagram. Their amorphous nature and intermediate range order was checked employing X-ray diffractometry (XRD), the short range order was characterized by extended X-ray absorption fine structure (EXAFS) (Ge and Se K absorption edge) and their microstructure was characterized by scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS).

The effect of silver content on the optical properties of films of Agx(Ge0.25Se0.75)100 − x (with x ≤ 25 at.%) chalcogenide glasses has been analysed. The films were prepared by pulsed laser deposition from bulk glass target. Morphology, structure and optical properties of the films were characterized by profilometry, X-ray diffraction and UV–visible–NIR transmission spectroscopy (wavelength 400-2500 nm). Refractive index, absorption coefficient, and the optical band gap energy were determined. It was found that the refractive index increases (for every wavelength) whereas the optical band gap energy decreases as the silver content increases. Fil: Conde Garrido, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina Fil: Piarristeguy, A.. Universite Montpellier II; Francia. Centre National de la Recherche Scientifique; Francia Fil: Ureña, Maria Andrea. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina Fil: Fontana, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina Fil: Arcondo, Bibiana Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina Fil: Pradel, A.. Centre National de la Recherche Scientifique; Francia. Universite Montpellier II; Francia

GexSe1−x system is a well-known glass former for x ≤ 0.43. The addition of third elements (i.e. Ag, Sb, and Sn) even up to high concentrations is possible without affecting its glass forming ability. These metals confer these glasses very particular properties. Ag–Ge–Se glasses are semiconductors for low Ag concentration whereas they are fast ionic conductors above 8 at.% Ag. The structure, thermal behaviour and transport properties of these glasses are analyzed. Metal doping is easily performed in chalcogenide glasses. It has been observed that, in contrast to crystalline semiconductors, their transport properties were not substantially affected as the valence bonds of the doping elements are completely saturated. The resource of doping with a 57Fe probe is widely employed in the materials study in order to characterize the short-range order of their structure by means of Mössbauer effect spectroscopy. These results are discussed and correlated to the structure and morphology of this chalcogenide system. Fil: Ureña, Maria Andrea. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina Fil: Fontana, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina Fil: Piarristeguy, A.. Centre National de la Recherche Scientifique; Francia. Universite Montpellier II; Francia Fil: Arcondo, Bibiana Graciela. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Fisica. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería; Argentina; Argentina

El propósito de este artículo es revisar desde una perspectiva crítica el uso de la noción de mercado en obras recientes de historia económica. En las mismas aparece muchas veces utilizada en análisis que rigurosamente consideramos no constituyen fenómenos de aquellos que la teoría económica explica. Otras veces se recurre a fomas adjetivadas de la noción de mercado. Tomaremos como ejemplo de esas formas, las del mercado interno y mercado nacional, teniendo en cuenta su utilización en obras de historia económica. Trataremos de demostrar la génesis de esas nociones y su utilización en el discurso histórico, asi como señalar la fecundidad de esas categorías si se insertan en un esquema, no prescinda de la teoría sino que enriquezca con su sistema de relaciones. La pretensión final es señalar el origen de ciertas categorías utilizadas en la explicación histórica y el hecho de que a pesar de no constituir una teoría o cuerpo de teorías, sin embargo, ejercen un poderoso atractivo en aquellos investigadores que dificilmente aceptan la ausencia de la misma en la explicación histórica. Es finalidad reivindicar la teoría económica como herramienta única y necesaria para hacer comprensible aquellos fenómenos de los que se ocupa la historia económica.

In this work, the structure of Fe and Sn doped Agx(Ge0.25Se0.75)100−x (x=0 to 25 at.%) intrinsically inhomogeneous glasses is analyzed employing 119mSn and 57Fe Mossbauer spectroscopy, X-ray diffractometry and scanning electron microscopy. 119mSn enters in the glass as a substitutional impurity for Ge whereas 57Fe enters as an interstitial impurity. Mossbauer spectra obtained with 119mSnO3Ca source, from samples containing about 1% 119Sn for Ge, reveal that the local order of Ge in both amorphous phases is basically the same whereas Mossbauer spectra obtained with 57Fe(Rh) source, from samples containing about 0.5% 57Fe, evidence the differences between both phases.

X-ray and Mössbauer studies are performed on (Mg70Zn30)100-xSnx rapidly colled alloys with different tin contents. The third element (Sn) added to Mg70Zn30 modifies the glass forming ability (GFA) of the binary alloy. It is shown that this occurs because of the appearance of an intermetallic compound (Mg2Sn) that perturbs the crystallization of the remnant MgZn. The large affinity of the added element (Sn) to one of the components (Mg) appears to be the key to the improved GFA. Structural similarities were found between the obtained glass and amorphous Mg70Zn30.

Mossbauer spectroscopy and X-ray diffraction studies were performed on rapidly quenched samples of MgCuSn and MgZnSn ternary alloys, for different tin concentrations, in order to investigate the influence of tin on the glass-forming ability of Mg-based binary alloys. It was found that the addition of tin atoms, which have a large association tendency with Mg atoms, increases the disorder favoring the formation of amorphous phases. This effect is due to the presence of configurations with a Mg 2 Sn type structure which have a small chemical interaction with the remnant MgCu and MgZn material. These associations obstruct the crystallization of such remnant matrices and extend their glass-forming composition range.

Solid samples of (SnkGe1− k)36Cu64 with different tin concentrations were produced by the Splat Cooling technique. The melted material was cooled down from different initial temperatures (T0). These samples were analyzed by Mössbauer spectroscopy and X-ray diffraction. The results are compared with those obtained in similar measurements on the annealed samples and on the slowly cooled material. The fast quenched samples were all polycrystallines. The resultant phases are analized and a memory effect of the liquid state in the solid material is discussed.

XRD and Mosbauer studies on (Mg70Zn30)100-xSnx alloys with various tin contents indicate the appearance of Mg2Sn clusters that modifies the glass forming ability compared to the binary alloy.